1. Field of the Invention
This invention relates generally to an automotive power supply, and more specifically to an automotive power supply which is designed to boost the supply voltage to an auxiliary battery, in charging main and auxiliary batteries in parallel by a generator which produces a voltage when an engine is in operation, by compensating the line voltage drop between the generator and the auxiliary battery.
2. Description of the Prior Art
Most conventional types of power supplies used in automobiles for leisure purpose such as mobile homes, tent trailers, camping cars, etc. are generally equipped with a generator 1 producing a voltage when an engine is in operation, a main battery 3 for driving a starter motor 2, and an auxiliary battery 4 which serves as a power source for d-c electric equipment 5 in the automobile such as a pump motor, lighting, a refrigerator, etc., as shown in FIG. 1, having such a construction that the main and auxiliary batteries 3 and 4 are charged in parallel by the generator 1 when the engine is in operation, and that an isolator 6 comprising, for example, diodes is provided between the main and auxiliary batteries 3 and 4 to ohmically disconnect the electric circuit to prevent load of automotive electric equipment from being applied to the main battery 3, when an engine is stopped. Assuming the automotive d-c equipment 5 have a total rated current of approx. 10A, and a charging current of approx. 20 A is supplied to the auxiliary battery 4 in this type of automotive power supply, a current of approx. 30 A is required to be supplied from the generator 1. However, the auxiliary battery 4 is usually located near the automotive d-c equipment 5 mounted in the container of a trailer, about 5 to 10 m distant from the main battery 3, so that the voltage generated in the generator 1 suffers a considerable voltage drop over the distance to the auxiliary battery 4, with the consequence that only a current of approx. 10 A is supplied to the auxiliary battery 4 and the automotive d-c equipment 5. In other words, the feeding efficiency from the generator 1 to the auxiliary battery 4 and the automotive d-c equipment 5 is lowered by the voltage drop. In addition, the charging efficiency of the auxiliary battery 4 is also deteriorated to such an extent that the auxiliary battery 4 cannot be charged to a desired voltage level. Particularly when a refrigerator and other equipment which is continuously operated are equipped in the automobile, the auxiliary battery 4 can hardly be charged. In view of this, conventional types of automotive power supplies usually have such a construction that the auxiliary battery 4 is charged from the commercial a-c power 8 using a rectifier 7, or an engine generator 9 is equipped independently of the generator 1 to supply sufficient current to the auxiliary battery 4 and the automotive d-c equipment 5 by supplementing a voltage equivalent to the voltage drop between the two batteries 3 and 4. However, because engine generators are generally large in size and expensive, they cannot suitably be used in small cars. Therefore, it is desired to provide a device which is able to sufficiently charge an auxiliary battery and which is less expensive then the conventional engine generator.